Leach’s Storm-Petrel: Status, Seasonal Occurrence, Geographic Distribution & Identification

*Leach’s Storm-Petrel Oceanodroma leucorhoa

Status: Rare to fairly common visitor in late spring to early fall in offshore Gulf of Mexico waters.

TX Status: There are 30 documented records for the state, some involving multiple birds. 2015 update: An unprecedented 100+ records of Leach’s Storm-Petrels occurred on August 29, 2015. 

Habitat: widespread species occurs in Pacific, Atlantic, and Indian Oceans.

Similar Species: Leach’s Storm-Petrel is very similar to the more common Band-rumped Storm-Petrel. Best clues are flight style and rump pattern. Leach’s flight style is nighthawk-like, with deep, erratic wingbeats whereas Band-rumps fly with steady wingbeats and arcing glides. Leach’s also generally shows a broken white rump and a more pronounced forked tail (although both of these features can be tough to see at sea).

*Texas Review Species, requiring written or photographic documentation.            © Copyright  Brad McKinney  31 October 31, 2004 (Status updated by Garett Hodne Nov 2014 )

SEASONAL OCCURRENCE GRAPH OF LEACH’S STORM-PETRELS:

The graph below shows the number and date of all Leach’s Storm-Petrel sightings on all Texas Pelagics from 1992 to 2015:

LESP Graph2


 

LEACH’S STORM-PETREL – TEXAS PELAGICS SIGHTINGS DISTRIBUTION:

This map shows the geographic distribution of Leach’s Storm-Petrel sightings (orange stars) on 27 Texas Pelagics mostly from South Padre Island, but also includes 1 trip from Port Aransas and 2 trips from Port O’Connor. Sighting coordinates from the remaining 25 + Texas Pelagics are not available.

Leach’s Storm-Petrel are predominately found beyond the shelf edge in deep pelagic waters than are Band-rumped Storm-Petrels


View Storm-Petrels in a larger map

Click on the box in the upper left of the map to view the map legend.

Click on each sighting symbol and the data label will appear showing the time, date and the number of birds seen.

Click on the link on the bottom of the map to view a larger map

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IDENTIFICATION of LEACH’S STORM-PETREL:

Cameron Cox a well known seabird expert and co-author of “Peterson Reference Guide to Seawatching – Eastern Waterbirds in Flight” commented on the Texas Pelagics Facebook Group about the ID differences between Leach’s and Band-rumped Storm-Petrels.

August 15 at 11:30am
“The rash of Leach’s Storm-Petrels on Texas Pelagics this summer has been interesting. It has also brought to light something I’ve been thinking about for several years, the identification and distribution of large storm-petrels found in the Gulf of Mexico during the summer. Since seeing photos of several heavily worn and molting Leach’s Storm-Petrels that were identified as Band-rumpeds on a Louisiana pelagic as well as a few similar birds from other locations in the Gulf, but rarely seeing images of similarly tattered Leach’s from areas on the Atlantic Coast I’ve thought about these birds and have come up with a two-parted hypothesis.

A. The Gulf hosts a number of 1st-cycle Leach’s Storm-Petrels in the summer (birds born the previous year), probably in much higher numbers than is currently recognized.
B. They are sometimes, possibly frequently, misidentified as Band-rumpeds

The reason for the confusion is multifaceted but really comes down to the fact that Band-rumped is the expected species in the Gulf and many of the traditional field marks for Leach’s are obscured on these molting/heavily worn 1st cycle birds. It particular the forked tail of Leach’s can be obscured do to molt or extreme wear. This fact is not mentioned in any of the ID literature I’ve reviewed. Also the dark line on the rump is often far less obvious on these 1st cycle birds. The pale ulnar bar can also be less obvious and fail to meet the bend in the wing during this period due to molt or wear. Finally a bird in primary molt or with tattered flight feathers is likely to have a very different flight style than a bird with a full set of wing feathers.

What traits are useful if some of the most well-known field marks are shaky on these first-cycle birds?

The traits used in the field will likely differ from those used for photos, but this what I’ve come up with from looking at photos.

1. The color of the back/nape seemed to be the most useful trait. In Leach’s the back color is a cold-toned gray to gray-black. This coloration seems particularly noticeable just where the head meets the body. This grayish color contrasts slightly with the darker wings (excluding the ulnar bar). Band-rumpeds are more uniform, lacking the contrast between back and wings. Worn birds in strong light can show a slight foxy brown color, a warm color, not cold-toned like Leach’s. Some photos of Band-rumped seem to show a faint grayish color on the head, but which taxon of the complicated mire currently referred to as Band-rumped Storm-Petrel these grayish birds belong to and whether they can occur in the Gulf I’m not sure. Even these slightly gray-toned Band-rumpeds lack the contrast between the back and wings typical of Leach’s as far as I can tell. Unlike many of the other traits, the gray back of Leach’s seems to be enhanced on worn birds and less apparent on fresh adults. How useful this is when looking at a bird in the field I’m not sure, but it shows well in photos. Check this on the large number of storm-petrel photos that have been posted here this summer.

2. The bill length is more subtle but still useful. Longer on Leach’s with a slightly hooked tip and more noticeable bump on the nostrils. In Band-rumped the bill looks slightly shorter and usually seems to have a more uniform shape, blunt-tipped and the bump at the nostrils is smaller and often not evident. This is something I only picked up recently looking at some of the photos taken on the last two Texas pelagics and I strongly suspect it would be extremely hard to judge in the field, though it can be judged in photos.

3. Different aspects of structure are subject the degree of molt shown, but there are differences still. Overall Leach’s are rangier and more angular with a watered-down Bulwer’s Petrel-like appearance. Band-rumped is more compact, with the wings held straighter, proportionally slightly broader winged with blunter-tips than Leach’s. The overall appearance is sort of halfway between a Leach’s and a Wilson’s Storm-Petrel. Even in molting Leach’s that do not show a fork in the tail appear longer-tailed than Band-rumped. The hand looks longer in Leach’s than Band-rumped though a Leach’s molting outer primaries would give a very different appearance.

4. The white rump patch is longer than it is wide in Leach’s but the reverse is true in Band-rumped.

5. Despite the potential for ambiguity that a bird in molt can present, flight style is still potentially useful. Usually Leach’s has more exaggerated wingbeats and the flight is bounding and buoyant. Gaps in the wing might reduce the buoyancy in the flight of Leach’s but the wingbeats still should be deep, potentially deeper than normal with faster wingbeats. Band-rumps tend to fly like small Pterodroma petrels, arching up and down on set wings with few shallow wingbeats interspersed. I expect that molt gaps might affect the flight style of Band-rumps more than Leach’s though this is less of an issue since many of the Band-rumps in the Gulf in mid to late summer seem to show little to no molt. Hypothetically though the wingbeats of heavily worn and molting Band-rumpeds would likely be deeper and more frequent than normal.
It would be very interesting to hear from observers on the last Texas pelagic on the flight style of the many Leach’s that were seen and how much the flight style of the Band-rumps seen stood out from them.
I hope this issue can be fleshed out more thoroughly. Any comments from people that have looked at these birds would be appreciated.”

LEACH’S STORM-PETREL PHOTOS

Leach’s Storm-Petrel (Oceanodroma leucorhoa) Here is a sequence of 7 rapid fire photos of the same Leach’s Storm-Petrel. All the diagnostic field marks can be seen. the deeply-forked tail, the dusky dark stripe that splits the white rump, the bold upperwing bands, the long pointed wings that extend high above the body during flight (like a nighthawk)

Leach's Storm-Petrel (Oceanodroma leucorhoa)
Photo 1; Date-Time: 20150829-101421-2
Leach's Storm-Petrel (Oceanodroma leucorhoa)
Photo 2; Date-Time: 20150829-101421-3
Leach's Storm-Petrel (Oceanodroma leucorhoa)
Photo 3; Date-Time: 20150829-101415-4
Leach's Storm-Petrel (Oceanodroma leucorhoa)
Photo 4; Date-Time: 20150829-101419-2
Leach's Storm-Petrel (Oceanodroma leucorhoa)
Photo 5; Date-Time: 20150829-101420
Leach's Storm-Petrel (Oceanodroma leucorhoa)
Photo 6; Date-Time: 20150829-101420-2
Leach's Storm-Petrel (Oceanodroma leucorhoa)
Photo 7; Date-Time: 20150829-101421
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